Vaillant Ecotec 937 Supply Gas Pipe Diameter/Exp Vessel

[marktaberham]

Hi,

We are planning to replace our current boiler and water tank, namely a Vaillant wall mounted THERMOcompact boiler and Vaillant Vantage VIH C120 sealed water tank.

After considerations from other threads and sales literature, I decided to seek quotes for the fitting of a Vaillant Ecotec 937. Following the heating engineers' visits, I was left with a few questions with which I was hoping the resident experts might be able to help with the following questions:

1. The diameter of the gas supply pipe from the gas meter to the current boiler is 22mm. The gas inlet diameter of the Ecotec 937 is 22mm. I estimate the gas supply run from the gas meter to the boiler to be 18-20m. Is the present 22mm supply pipe sufficient for the Ecotec 937?

2. The Ecotec 937 has an integral 10L expansion vessel. We have a 4-bedroom house with 2 bathrooms (1 with bath, 1 with shower) and 18 radiators. Could someone possibly tell me if the 937 expansion vessel is sufficient for this volume of water?

Thanks,

Mark

 

[gas4you]

1) No way. You will need at the very least 28mm all the way, possibly even 35mm for a substantial part from the gas meter.

2) I personally would add another exp vessel, probably around 12 litres.

Both of the above would be worked out by your RGI before quoting.

 

[marktaberham]

Dave,

Thanks for the reply. We have already had 4 quotes, and only one of the engineers mentioned the requirement for an additional expansion vessel and the possible requirement of an increase in the gas supply pipe diameter. I thought I'd ask the experts on here for a second opinion.

As a complete layman on these matters, is it possible for you to explain in noddy terms why the increase in pipe size is required? Is there a rule of thumb as to what to look for in required pressure in a boiler that would suit our current pipe size/length of run?

As the thought of the re-plastering/decorating through a hallway, dining room and utility room to replace our current gas supply pipe doesn't thrill me, could you recommend a suitable combi or boiler/water tank suitable for our requirements? Or would replacing the supply pipe be an easier job than I'm dreading?!!!

Thanks very much again,

Regards,

Mark

 

[Gasguru]

Personally I think you are making a BIG mistake in going down the combi route. Remember with a hot water cylinder you have a backup immersion heater when the boiler breaks down (and modern boiler quality is at an all time low). A 4 bed family house deserves better than a combi.

Gas regulations state the maximum pressure drop from gas meter to appliance inlet should be no more than 1 mbar. Many boilers will not operate correctly is the gas pressure is low.

Due to the fact that gas pressure is very low (about 100 times smaller than a car tyre) friction in the pipe will cause a significant pressure loss if the pipe is not of sufficient size. Your proposed combi consumes approximately 50% more gas than your existing heat only boiler therfore requiring a larger pipe. Undersized gas pipe is illegal and can be dangerous. Ignore tha gas fitting on the boilers inlet ..it has absolutely NOTHING to do with the gas pipe size required (I wish manufacturers would stop quoting it but they know the public and dumb installers think a smaller gas pipe size will make do). No combi will operate on your existing 22mm supply...it's too small and the pressure drop will be greater than 1 mbar.

An additional expansion vessel will add no more than £25.00 to the cost. It will prevent the system pressure from increasing too much when the heating is on. This helps reliability (since the system pressure does not fluctuate significantly from cold to hot) and in addition you will not have to top up the system so often.

 

[marktaberham]

GasGuru,

Thanks for the information - I had no idea mains gas pressure was so low. A rethink is in order - thanks for your help.

Regards,

Mark

 

[ChrisR]

We are planning to replace our current boiler and water tank, namely a Vaillant wall mounted THERMOcompact boiler and Vaillant Vantage VIH C120 sealed water tank.

You can still get the bits, and ANYTHING you replace these with will probably be inferior! The cylinders don't last forever I suppose if you don't replace the anode, but those boilers do!

 

[marktaberham]

ChrisR,

Thanks for your comments. Repair and a service of our current boiler, rather than replacement, are definitely on the agenda following your, and the other experts, helpful replies.

Regards,

Mark

 

[gas4you]

Don't forget though, if you do decide to replace, you will need to do both, as the Vantage cylinder can ONLY be used with your type of Vaillant boiler.

 

[garygttdi]

Is it possible/legal to run my new feed behind coving,as like others I need to run through the dinning room and the kitchen to get to the boiler.
Will 28mm fit behind a conventional bit of coving,anyone tried?

Current run leaves the meter in 22mm but arrives at the boiler in 15mm,although I lose the pipe about 2 foot from the meter as it disapears into a wall.

 

[Doctor Drivel]

1) No way. You will need at the very least 28mm all the way, possibly even 35mm for a substantial part from the gas meter.

28mm all the way? "at least" too, so some 35mm as well!!! What tripe!!!

2) I personally would add another exp vessel, probably around 12 litres.

It depends on the water capacity of the existing system. You don't guess it.

This is the problem with people who can't do thing properly and go by rule of thumb.

 

[Doctor Drivel]

Personally I think you are making a BIG mistake in going down the combi route. Remember with a hot water cylinder you have a backup immersion heater when the boiler breaks down (and modern boiler quality is at an all time low). A 4 bed family house deserves better than a combi.

More garbage! He can have an in-line electric instant heater in the DHW draw-off pipe for backup. Fine while the system is down. There is also the kettle, dishwasher and w/machine with their own heaters too.

Gas regulations state the maximum pressure drop from gas meter to appliance inlet should be no more than 1 mbar. Many boilers will not operate correctly is the gas pressure is low.

Due to the fact that gas pressure is very low (about 100 times smaller than a car tyre) friction in the pipe will cause a significant pressure loss if the pipe is not of sufficient size. Your proposed combi consumes approximately 50% more gas than your existing heat only boiler therfore requiring a larger pipe. Undersized gas pipe is illegal and can be dangerous. Ignore tha gas fitting on the boilers inlet ..it has absolutely NOTHING to do with the gas pipe size required (I wish manufacturers would stop quoting it but they know the public and dumb installers think a smaller gas pipe size will make do). No combi will operate on your existing 22mm supply...it's too small and the pressure drop will be greater than 1 mbar.

It is clear these people cannot use simple tables to work out gas pipe sizes.

An additional expansion vessel will add no more than £25.00 to the cost. It will prevent the system pressure from increasing too much when the heating is on. This helps reliability (since the system pressure does not fluctuate significantly from cold to hot) and in addition you will not have to top up the system so often.

That's if he needs one of course which has not been determined.

 

[Doctor Drivel]

1) No way. You will need at the very least 28mm all the way, possibly even 35mm for a substantial part from the gas meter.

28mm all the way? "at least" too, so some 35mm as well!!! What tripe!!!

Looking at some tables, I estimated about 8 to 9 metres of 28mm pipe from the meter, then the rest in 22mm for a 20 metre gas supply run for the 937 combi. And you put 28mm all the way? ..and maybe 35mmm?? My God!!!

2) I personally would add another exp vessel, probably around 12 litres.

It depends on the water capacity of the existing system. You don't guess it, you calculate it.

This is the problem with people who can't do things properly and go by rule of thumb.

 

[Doctor Drivel]

Dave,

Thanks for the reply. We have already had 4 quotes, and only one of the engineers mentioned the requirement for an additional expansion vessel and the possible requirement of an increase in the gas supply pipe diameter. I thought I'd ask the experts on here for a second opinion.

As a complete layman on these matters, is it possible for you to explain in noddy terms why the increase in pipe size is required? Is there a rule of thumb as to what to look for in required pressure in a boiler that would suit our current pipe size/length of run?

As the thought of the re-plastering/decorating through a hallway, dining room and utility room to replace our current gas supply pipe doesn't thrill me, could you recommend a suitable combi or boiler/water tank suitable for our requirements? Or would replacing the supply pipe be an easier job than I'm dreading?!!!

Thanks very much again,

Regards,

Mark

Look at this:
http://www.cda.org.uk/megab2/build/pub124/sec3.htm

In a 20 metre run for a 937 about 8 to 9 metres of 28mm from the gas meter and the rest in 22mm.

Take no notice of arm wavers, look at the tables. If your installer says 28mm all the way give him this link.

 

[gas4you]

OP, I haven't a clue what drivel is drivelling on about in these last posts, as like most on here who know what we are talking about I have him added to my ignore list, so I can only guess it is some dangerous c r a p as usual.

As always ask him directly how many gas appliances he has actually fitted to gain his knowledge? Answer = ZERO

What ever he says is just gleaned from the internet search engines, nothing else

 

[Doctor Drivel]

OP, I haven't a clue what drivel is drivelling on about i

It is clear this arm waver hasn't a clue how to size up a gas pipe. The word "Cowboy" comes to mind.